Ongoing concerns about improving quality and access to care to the low- income population, have been compounded by fiscal stresses facing providers and public payers of health care for the indigent. These factors have resulted in calls to reform public health financing and delivery systems. While action has been taken, usually in the form of managed care, there is a paucity of information regarding the factors that affect patient choice of the site of care. This study seeks to explore the association of population characteristics, availability and convenience of health care, and experience with health care with the selection of site of illness-related ambulatory care (office-based physician, hospital outpatient department, nonhospital clinic, or emergency department) for the nonelderly, low-income population. The primary focus of this dissertation will be the role of type of insurance and site of and relationship with the regular source of care, because these factors are sensitive to changes in health policy. This analysis will be based on the 1987 National Medical Expenditure Survey, a nationally representative sample of 35,000 respondents in 14,000 households. Specifically, this dissertation has the following objectives: 1. to describe differences in site of diagnostic and treatment care for the low-income population compared those with higher incomes; 2. to identify the factors that are associated with selection of site of diagnostic and treatment care for the low-income, nonelderly population; and 3. to determine the extent to which these factors, particularly insurance and regular source of care drive the choice of site of diagnostic and treatment care. A greater understanding of the components that influence the site of care, can provide policymakers and program planners with the knowledge to make more informed and effective policy decisions regarding the organization and delivery of care to the low-income population.